1. Field of the Invention
This invention relates to the field of metallurgy, and in particular to a smelting reduction facility, and more particularly to a prereduction furnace of a smelting reduction facility of iron ore.
2. Description of the Related Art
In a smelting reduction facility of iron ore, the facility is generally divided into two major furnaces which are a prereduction furnace and a smelting reduction furnace. The smelting reduction furnace is usually a convertor type reaction vessel. In the smelting reduction furnace, iron ore and a carbonaceous material are fed to a molten iron bath and oxygen is blown into the bath from above the bath through a lance, by which the iron ore is reduced by a smelting reduction reaction. In the prereduction furnace, the iron ore to be fed to the smelting reduction furnace is prereduced by an exhaust gas from the smelting reduction furnace. The prereduction furnace is of a fluidized bed type in which the exhaust gas from the smelting reduction furnace is utilized for fluidizing and reducing the iron ore since the process is economical.
In this fluidized bed process, a bubbling fluidization bed process is excellent in engineering maturity and can advantageously prevent the attrition of the iron ore in its preheating and reduction. FIG. 1 is an explanatory illustration of a smelting reduction facility. As shown in FIG. 1, the smelting reduction facility comprises of the smelting reduction furnace 1, the prereduction furnace 2 which prereduces the iron ores which are to be fed to the smelting reduction furnace 1, the storage bin 3 for a main raw material, i.e., iron ores, and the storage bin 4 for auxiliary raw materials.
The smelting reduction furnace 1 comprises a convertor type reaction vessel 5, the lance 6 inserted through the top opening 5a of the reaction vessel 5, the gas injection nozzles 7 through which a stirring gas is injected into the metal bath, the chute 9 for feeding the prereduced iron ores installed at the hood 8 and the chute 10 for feeding the auxiliary raw materials also installed at the hood 8.
The prereduction furnace 2 comprises a distributor 12 incorporating a large number of nozzles 13, the gas blowing chamber 14 at the bottom of the distributor 12 and the prereduction chamber 15. In the gas blowing chamber 14 the gas inlet 16 is installed. In the prereduction chamber 15 the chute 17 for feeding the iron ores and the gas exhaust outlet 18 are installed.
The prereduced ores are introduced to the discharge pipe 19 via the discharge hole 12a installed at the center of the distributor 12. The discharge pipe extends downward through the bottom of the prereduction furnace 2 and is connected to the supply chute 9 via the L-shaped valve 20 and two intermediate storage bins 21. The gas outlet 11 installed at the hood 8 is connected to the gas supply pipe 22 which is connected to the gas inlet 16 via the dust collecting cyclone 23. The gas exhaust outlet 18 is connected to the gas exhaust pipe 24 which is connected to the dust collecting cyclone 25.
The duct 26 connects the storage bin 3 to the chute 17 for the prereduction chamber 15. The duct 27 connects the storage bin 4 for the auxiliary raw material to the chute 10.
A predetermined quantity of the molten pig iron 28 is accomodated in the smelting reduction furnace 1. The iron ores, after being prereduced in the prereduction furnace 2, are fed to the smelting reduction furnace 1.
The auxiliary raw materials such as coal and flux are fed to the smelting reduction furnace 1 via the chute 10.
Oxygen is blown into the convertor type reaction vessel by the lance 6 vertically inserted through the top opening 5a of the vessel 5. The stirring gas such as nitrogen is injected into the molten pig iron 28 by the gas injection nozzles 7. Carbon monoxide gas is generated by the reaction between the carbon from the carbonaceous material like coal fed to the smelting reduction furnace and the carbon in the molten pig iron 28, and the oxygen gas introduced through the lance 6. A portion of the generated carbon monoxide gas reacts with the excess oxygen introduced through the lance 6 to generate carbon dioxide gas. The iron ores fed into the molten pig iron 28 are melted and reduced by the generated heat in the above-mentioned exothermic reactions and by the reduction agent, i.e., carbon and carbon monoxide gas specified above.
The high temperature exhaust gas from the smelting reduction furnace 1 is discharged from the gas outlet 11 installed at the hood 8, passing through the gas supply pipe 22 and introduced into the gas blowing chamber 14 of the prereduction furnace 2. The high temperature gas is injected into the prereduction chamber 15 through the nozzles 13 of the distributor 12 and preheats and prereduces the iron ores which are fed from the storage bin 3 through the duct 26 and the chute 17.
The prereduced iron ores are introduced to the discharge pipe 19 via the dischage hole 12a installed at the center of the distributor 12 and fed to two intermediate storage bins 21 via the L-shaped valve 20. The prereduced iron ores are alternatively fed to these storage bins and temporarily stored therein. The prereduced iron ores are alternatively discharged from these bins into the smelting reduction furnace 1 through the chute 9. Thus the iron ores are prereduced before the smelting reduction reaction, which enhances the thermal efficiency of the process.
FIG. 2 is a vertical sectional view of the distributor 12. As shown in FIG. 2, the distributor 12 is made of a ceramics, the top surface of which is concave. A plurality of the nozzles 13 are installed in the distributor 12 surrounding the discharge hole 12a.
The distributor 12 is made of a ceramics which is heated by the high temperature gas from the smelting reduction furnace 1 injected by the nozzles 13 into the prereduction furnace 2. The high temperature gas contains dust such as fine particles of iron ore having a size under 10 micrometers which cannot be removed by the dust collecting cyclone 23 shown in FIG. 1. These dust particles contain alkali compounds having Na and K which is sticky in the high temperature gas having the temperature over 900.degree. C. These dust particles stick to the comparatively rough bottom surface 12b of the distributor 12 and to the inside surface of the nozzles 13 and are heated by the accumulated heat in the distributor and are sintered hard. Thus, the stuck dust particles gradually accumulate on the surfaces of distributor 12 and the flow of the gas is so much disturbed that a normal fluidizing can not be continued.